Support structure



w. F. SWIGER 3,044,561

SUPPORT STRUCTURE July 17, 1962 Filed June 10, 1957 3 SheetsSheet 1F/G./. F/6.2.

INVENTOR. WILL/AM F. SW/GER ATTORNEYS July 17, 1962 w. F. SWIGER3,044,551

SUPPORT STRUCTURE Filed June 10, 195'? 3 Sheets-Sheet 2 INVENTOR.WILL/4M F. SW/GER 5%J1/Zh5/744 FIG. 5.

United rates This invention relates to structures for supporting aplatform above the surface of a body of water.

Co-pending application Serial'No. 553,567, filed December 16, 1955,discloses an elongated tripod support structure with hollow legs adaptedto be floated horizontally in a body of water and towed to a desiredlocation. The legs of the structure are adapted to be flooded at one endat a controlled rate so that the flooded ends sink and tilt thestructure toward an upright or vertical position. Flooding of thestructure is continued until it rests firmly on bottom.

This type of structure is ideally suited to be transported to differentlocations and erected to support various types of equipment above a bodyof water. For example, it can be used to support drilling equipment foroffshore wells, or it can be used to support electronic equipment suchas that used for offshore radar stations. The struc ture has theadvantage that it can be dewatered and tilted from a vertical to ahorizontal position so that it may be towed easily from one location toanother.

When the structure is to be erected in relatively deep water and used tosupport heavy equipment such as a drilling rig, the structure must befirmly anchored on the formation under the water.

This invention provides an apparatus for improved anchoring of offshorestructures having at least one hollow leg.

In terms of method, one aspect of the invention contemplates anchoring ahollow leg structure in a formation under a body of water by positioningthe structure in an upright position in the water with the lower end ofthe legs resting on the formation. At least one hollow leg is filledwith a fluid heavier than the water in which the structure is located sothatthe structure is anchored firmly to the formation.

In terms of apparatus the invention includes a hollow leg structureadapted to be floated horizontally in a body least one hollow leg to addto the stability of the struc If the structure is to be anchoredpermanently. in place, say as a permanent radar installation, the heavyfluid Zis concrete or some similar mate'rial which takesa permanent setand adds to the strength of the structure. Ifthe structure is to bemoved from one location tosanother, the fluid is of such a nature thatit does not take a permanent set. For example, the fluid could be aconcentrated heavy salt solution such as zinc chloride.

If the structure is used in drilling an offshore Well, preferably theheavy fluid is drilling fluid used in drilling the well. Disposeddrilling fluid in at least one of the legs of the structure aids infirmly anchoring the structure in place, and stores a large amount of.weight in a position to provide a'low center of'gravity,therebyincreasing the stability of the structure and reducing the Weightwhich must be supported by a platform on the upper end of the structure.This is an important advantage because at times the weight of thedrilling mud can Patented July 17,- 1962 amount to as much as half theload which would have to be supported by the platform if the mud werenot stored in at least one of the hollow legs.

Depending on the depthand size of the well being drilled, the amount ofdrilling fluid required can vary between 500 and 1500 barrels. If a wellrequires 1,000 barrels of mud weighing 11 pounds per gallon, the totalWeight of the mud is about 230' tons. By storing a substantial portionof the mud in at least one of the legs, a considerable load is taken offof the drilling rig platform, and at the same time, the stability of thestructure is also increased. Moreover, the drilling mud does not take apermanent set and can easily be flushed from the legs when the structureis to be moved.

In terms of apparatus for drilling an underwater well, the inventioncontemplates a support structure resting on a formation under a body ofwater and extending toward the water surface. The structure includes atleast one hollow leg in which a drilling fluid is stored, and a drillpipe is supported from the structure to extend down into a well beingdrilled. Conduit means are provided for connecting the upper end of thedrill pipe with the hollow leg, and conduit means are-provided forconnecting the hollow leg with the annular space between the drill pipeand the well so that drilling mud can be circulated from the hollow legthrough the drill pipe and back to the hollow leg.

In terms of method for drilling an underwater well from a hollow legstructure resting on.a formation under a body of water, the inventionincludes the steps of forming a hole in the formation with a drill pipesupported by the structure. A drilling fluid is disposed in at least onehollow leg in the structure, and circulated from the leg through thedrill pipe and back into the hollow leg. 7

These and other aspects of the invention will be more fully understoodfrom the following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a side elevation of a hollow leg support structure floatinghorizontally in a body of water;

FIG. 2 is an end view of the structure shown in FIG. 1;

FIG. 3 is a schematic side elevation, partially broken away, showing thestructure of FIG. 1 being tilted toward a vertical position by floodingone end of the legs of the structure; v i I FIG. 3A is a side elevationof the structure of.FIG.v l

flooded to rest in a vertical position on the, bottom of the water body;I

FIG. 4 is a schematic elevation, partially broken away, of the structureof FIG. 1 resting in an upright position on the underwater formation andsupporting a'tits upper end a platform and drilling rig being used todrill a well in the formation; i

FIG. 5 is an enlarged view taken online 5-5, of FIG. 4 showing howdrilling fluid is circulated from one of the hollow legs into the wellandbackfto the hollow g; v FIG. 6 is a schematic sectional elevation ofthe hollow leg in which drilling fluid is circulated and stored; and

"FIG. 7 is a view taken on line 7-7 of FIG. ';6. Referring to FIGS. v1and 2, the support comprises a pair or first set of parallel tubularlegs13, 14 (see FIG, 2) which are designated the lower legs, since theselegs are shown floating in a body of waterf15 when the struc I ture isin a horizontal position. A'n upperv or third leg 16 is connected toeach of the two lower legs byhollow tubular buoyant bracing members 17so the'upperleg is parallel to and equidistant from the other two legs.The tubular members are arranged ina K-brace system and the two lowerlegs are connected to each other by an identical arrangement so thateach leg is equidistant from the other two. i

A temporary truss 18 is mounted across the ends of the legs which willbe the upper ends when the structure is in an upright position. Unlessotherwise indicated, throughout the remainder of the description theterms upper and lower are used to indicate relative positions when thestructure is in an upright position.

Referring to FIG. 6, leg 14 is shown in detail, and since all three legsare identical, a description of this leg will suflice :for the othertwo. Starting at the lower end, the leg has a plurality oflongitudinally spaced transverse diaphragms 19A, 19B, 19C, 19D, etc.,dividing the leg into separate compartments 20A, 20B, 20C, 20D, etc., inascending order. Compartment 20A is connected to compartment 20B by aconduit 24 extending through the upper (when the leg is in a horizontalposition) edge of diaphragm 19A into compartment 2trB. A similarlylocated conduit 26 connects compartment 20B with compartment 20C, and soon to the uppermost compartment which is sealed at its top by a cap 27.

A valve 28 within the lower end of compartment 20A is adapted to becontrolled by a pneumatic line 29 extending to the upper end of the legto admit water to the compartment 20A. The lower end of leg 14 is closedwith'acover plate 32.

Four elongated symmetrically spaced tubular pile guides 42 extendlongitudinally throughout the length of the legs, and each guide extendsthrough and is welded to the respective diaphragms to effect fluid-tightseals for the compartments. 7

An air line 46 extends through the cap on the upper end of the structureand is adapted to receive compressed air from a supply (not shown) topressure the compartments and control flooding or dewatering of the leg.

The upper end of each pile guide terminates just above the cap on theupper end of the leg, and is sealed thereto by welding. These ends ofthe pile guides are closed by temporary plugs (not shown) when thestructure is floated horizontally in the water. The lower ends of thepile guides are welded around openings 50 in the cover plate sliding fitinside the pile guides, are driven into the bottom of the Water body bypile driving means (not shown) on the temporary truss to anchor thestructure firmly in place.

If the structure is to be used to support a permanent radarinstallation, for example, the legs are filled with a concrete slurry(not shown) which is allowed to set to give the structure additionalweight to anchor it to the formation and at the same time increase thestrength of the legs. The piles and pile guides in the legs serve toreinforce theconcrete and provide additional strength for the structure.

0n the other hand, if the structure is to be used for V drilling, asshown in FIG. 4, a floating barge or platform on the lower end of theleg. The openings are sealed by knock-out plugs 51. The lower end ofeach of the pile guides (see FIG. 6) has holes 52 to vent the interiorof the pile guides to compartment 20A. The knock-out plugs are lightlywelded in place so they may be readily knocked off by piles 55 (see FIG.4) which may be driven down through the pile guides and out the lowerend of the legs when the structure is resting on a soft bottom.

To tilt the structure from a horizontal to a vertical position, acontrolled amount of water is admitted to the end of each of the lowerlegs which is to rest on the bottom. Referring to FIG. 3, the structurestarts tilting to- 64 adapted to support a drilling rig 65 is thenfloated into the space between the upper ends of the legs and hoistedabove the. water on support rods 66. One of. the pile guides in at leastone of the legs, and preferably in each of the legs, is kept open by notdriving a pile down it. Water is displaced from each of the legs bypumping a drilling fluid or mud (not shown) down the open pile guide.The mud is heavier than the Water and adds to the stability of thestructure. A well 68 is drilled inthe formation with a string of drillpipe 70, and a surface conductor 72 is cemented in the well. Referringto FIG. 5, the surface conduct-or extends from the well up into a bore74 in the platform and terminates just below a rotary table 76 which issupported by the platform and powered by conventional means (not shown).Drilling fluid flows through a pick up conduit 78 in the upper end ofone of the legs of the structure, and is forced by a first pump 80through a drilling mud hose 82 into a swivel 84 suspended by a hoistingcable 86 which in turn is supported at the upper end of a derrick 88.The mud flows from the swivel down through a kelly joint 89 extendingthrough the rotary table and connected to the upper end of the drillpipe string. The mud flows out the bottom of the drill pipe, picks upcuttings formed in the well and flows back up the annular space betweenthe drill pipe and the surface conductor. A lateral conduit 90 in theupper end of the surface conductor discharges drilling fluid andcuttings on a shaker screen 92 which separates cuttings and drillingfluid so that the drilling fluid flows through the screen into a hopper94 and into a settling pit 96 in the platform. The cuttings slide oilthe screen and are either collected or discharged into the water. Avertical baffle 98 divides the settling pit into two sections, and themud from the well flows into a remote end of one of the sections. Themud then flows over the baflie into the other section Where it is pickedup through a conduit 99 and returned by a second pump 100 down the openpile guides connected by a coupling 101 and line 102 to-the ward anupright position. In the initial stages of flooding the two lower legsto start the structure tilting toward the vertical, the location ofconduits 24, 26, etc., in the diaphragms 19A, 19B, etc., insure thateach compartment 6 is completely flooded before flooding of thesuperadjacent compartment begins. Thus, substantially no air is trappedin the compartments and the flooding of the structure proceeds in anorderly and predictable manner.

If the cross bracing did not exert'a buoyant efiect as the structuretilts, the moment tending to cause the structure to tilt to a verticalposition would increase rapidly as the structure tilts, and smash theupperv leg into the water with a force which might cause injury topersonnel or damage to the structure. However, the buoyant crossbracingholds the tilting to a safe rate and permits the upper leg to enter thewater gently.

The two lower legs are flooded until the structure reaches a verticalposition, and then all three legs are gradually flooded to approximatelythe Water leveljto seat the structure firmly on the bottom. The plugsare re-.

moved from the upper end of each pile guide, if a soft second pump.

The settling pit provides a zone of suflicient quiescence for thedrillingmud to permit the settling 0t sand and relatively small cuttingswhich might not have been separated from the drilling mud by the shakerand screen. The mud jets from the openings 52 in the 'bottom of the lpile guide at a rate sufiicient to keep the mud in the bottom of the legthoroughly stirred. The mud then flows upwardly through the compartmentsin the leg where it is finally picked up again by the pick-upconduit'78. By

having the mud flow in an upward direction through the leg, the settlingof fine particles in the leg is prevented.

The other two legs may be used for storage or circulation of drillingfluid if required, and provide ideal storage space for standby emergencymud which might be required in the case of a threatened blow-out or lostcirculation. By storing the mud in the legs, a considerable bottom isencountered, and piles 55, which make a close 75 weight is relieved fromtheplatform, and the stability of the structure is increased. Moreover,the mud can easily be removed from the legs to permit the structure tobe moved to a new location.

If it is desired to remove the structure, the drilling platform islowered and towed away, the piles are disengaged at their lower endsbelow the lower ends of the legs of the structure, either beingdecoupled, jetted free, or cut by suitable means, such as shapedcharges. The lower ends of the pile guides are plugged with a packer 67(see the right hand pile guide in FIG. 6), the caps 27 are replaced andthe legs are dewatered or de-mudded in reverse order from that describedabove. Recovery of the structure proceeds in the reverse direction tobring the structure back to the horizontal position shown in FIG. 1. Ifthe legs are filled with a drilling mud or other material which is worthsaving, the mud may be recovered by pumping water down on top of the mudand forcing the mud up the open pile guide to the upper end of thestructure where it may be collected, say on a barge.

I claim:

1. An offshore apparatus for drilling holes in geological formationsunderlying a body of water, the apparatus comprising a unitary structurefloatable horizontally to a drilling site and sinkable in a verticalorientation to the bottom of the body of water at the site, thestructure having a set of laterally spaced-apart elongated rigid legswhich in vertical orientation extend from the bottom to above thesurface of the body of water, rigid braces between the legs, one of thelegs having a plurality of compartments along its length, thecompartments being in internal fluid communication, a platform supportedby the structure above the surface of the water, a drilling rig on theplatform comprising a casing extending downwardly to the formation and adrill pipe and a drill in the casing operated from the platform,drilling fluid in the communicating leg compartments, and meansincluding a drilling fluid delivery line extending from the uppermostcompartment to the rig and a drilling fluid recovery line extending fromthe rig to the lowermost compartment for circulating the fluid from theuppermost compartment, into and out of the hole by counterflowcirculation through the drill pipe and casing, and into the lowermostcompartment.

2. A unitary elongated support structure adapted to float horizontallyin a body of water over an underwater formation, the structurecomprising a set of elongated and laterally spaced hollow legs, bracesconnecting the legs together, at least one of the legs having closedinternal compartment means extending for a substantial distancelongitudinally within the said leg, means for flooding said internalcompartment means to tilt the structure from a horizontal to a verticalposition so it rests on the underwater formation, a drilling rig mountedon the upper end of the structure above the body of water when in thevertical position, the rig including a hollow depending drill pipe fordrilling a hole in the underwater formation, a

casing surrounding the drill pipe from the platform to at least thehole, and means including a drilling fluid delivery line connectedbetween the drill pipe and the com partment means and a recovery lineconnected between the casing and the compartment means for circulatingdrilling fluid serially out of the lower end of the drill pipe into thehole, upwardly through the casing, into the compartment means and back,into the upper end of the drill pipe.

3. A unitary elongated marine support structure adapted to floathorizontally in a body of water over an underwater formation, thestructure comprising a set of elongated and laterally spaced hollowlegs, braces connecting the legs together, at least one of the legshaving closed internal compartment means extending for a substantialdistance longitudinally within the said leg, means for flooding saidinternal compartment'means to tilt the entire structure from ahorizontal to a vertical position so it rests on the underwaterformation, drilling fluid disposed in the compartment means, a drillingrig mounted on the upper portion of the structure when in a verticalposition, the rig including a hollow depending drill pipe for drilling ahole in the underwater formation, a casing surrounding the drill pipe,and means including drilling fluid delivery conduit means connectedbetween the upper end of the drill pipe and the upper portions of thecompartment means and recovery conduit means extending from the upperend of the casing to the lower portions of the compartment means forcirculating drilling fluid serially from an upper portion of thecompartment means to the upper end of the drill pipe, downwardly throughthe drill pipe, out the lower end of the drill pipe, up through the holeand the casing, and out of the casing into a lower portion of thecompartment means.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.044 561 Julyl7 1962 William F. Swiger It is hereby certified that error appears inthe above numbered patent. requiring correction and that the saidLetters Patent should read as corrected below.

Column 1, line 65. for "Disposed" read Disposing column 3 line 34, for"pressure" read pressurize Signed and sealed ,this 18th day of December1962 (SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents

